Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Objectives • IdentifyEarth’s different geologic layers. • Explainhow the presence of magnetic bands on the ocean floor supports the theory of plate tectonics. • Describethe movement of Earth’s lithosphere using the theory of plate tectonics. • Identifythe three types of plate boundaries and the principal structures that form at each of these boundaries.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Bellringer A peach can be used as a model for some aspects of Earth’s structure. Compare the drawing of the cross section of the peach below with the cross section of Earth to its right, and answer the following questions.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Bellringer, continued 1. Describe the outer layer of the peach (the skin). What aspect of Earth’s structure does the outer layer of the peach represent? 2. The peach pulp is the next layer. How would you describe it? What aspect of Earth’s structure does the peach pulp represent? 3. The pit is the innermost part of the peach. What is the pit like? What aspect of Earth’s structure does the peach pit represent?

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 What is Earth’s Interior Like? • The Earth is made up of three layes: the crust, the mantle and the core. • Crust the thin and solid outermost layer of Earth above the mantle • Mantle the layer of rock between Earth’s crust and core • Core the center part of the Earth below the mantle

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Structure of the Earth

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Formation of Earth’s Crust, Mantle, and Core

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 What is Earth’s Interior Like? continued • Earth’s interior gets warmer with depth. • Geologists believe that the mantle is much hotter than the crust, reaching temperatures higher than 1250° C (2280° F). • The core is hotter than the mantle, reaching temperatures higher than 6000° C (10,800° F).

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Magma

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Magma and Vents

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 What is Earth’s Interior Like? continued • Radioactive elements contribute to Earth’s high internal temperature. • The breakdown of radioactive isotopes uranium, thorium and potassium give off energy that contributes to Earth’s high internal temperatures.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics • Around 1915, German scientist Alfred Wegener proposed the idea that the continents were once united as a supercontinent and then drifted apart. • He pieced the continents together like a puzzle and called the supercontinent they formed Pangaea. • Wegener found identical fossils on widely separate continents, which supported his idea.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Continental Drift (Pangaea)

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics, continued • Evidence for Wegener’s ideas came later. • Wegener’s theory of continental drift was ignored until structures discovered on the ocean floor provided evidence for a mechanism for the movement of continents. • Symmetrical bands on either side of a mid-ocean ridge indicate that the two sides of the ridge were moving away from each other and new ocean floor was rising up between them.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics, continued • Alignment of oceanic rocks supports the theory of moving plates. • Iron in molten rock aligns itself with Earth’s magnetic field as it cools. • The Earth’s magnetic field reverses polarity about every 200,000 years • The process is recorded as magnetic bands in rock, based on the age of the rock. • Symmetrical bands on either side of the Mid Atlantic Ridge suggest that the crust was moving away from the ridge.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics, continued • Earth has plates that move over the mantle. • The crust and upper portion of the mantle are divided into about seven large pieces called tectonic plates. • Lithosphere the solid, outer layer of Earth, that consists of the crust and the rigid upper mantle

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics, continued • Plate tectonics the theory that explains how the outer parts of Earth change through time, and that explains the relationships between continental drift, sea-floor spreading, seismic activity, and volcanic activity

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Tectonic Plates

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Tectonics, continued • It is unknown exactly why tectonic plates move. • One hypothesis suggests that plate movement results from convection currents in the asthenosphere, the hot, fluid portion of the mantle. • Another hypothesis suggests that plate movement results from the force of gravity acting on the plates.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Boundaries • Mid-ocean ridges result from divergent boundaries. • The border between two plates is called a boundary. • Divergent boundary a place where two plates are moving apart • New rock forms between divergent boundaries. • Magma liquid rock produced under Earth’s surface

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Divergent and Convergent Boundaries

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Convergent Boundary

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Boundaries, continued • Oceanic plates dive beneath continental plates at convergent boundaries. • Plates slide over each other at a convergent boundary. • Subduction the process by which one lithospheric plate moves beneath another as a result of tectonic forces • The area where one plate slides over another is called a subduction zone. Subduction zones produce ocean trenches, mountains, and volcanoes.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Subduction Zone

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Boundaries, continued • Subduction of ocean crust generates volcanoes. • Chains of volcanoes form on the upper plate in a subduction zone. • These volcanoes can form far inland from their associated oceanic trench.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Boundaries, continued • Colliding tectonic plates create mountains. • When two plates collide, mountains are formed at the boundary of the collision. • The Himalayas formed during the collision between the continental tectonic plate containing India and the Eurasian continental plate.

Section 1 Earth’s Interior and Plate Tectonics Chapter 21 Plate Boundaries, continued • Transform fault boundaries can crack Earth. • Plate movement can cause breaks in the lithosphere. • Fault a crack in Earth created when rocks on either side of a break move • Plate movement at transform fault boundaries is one cause of earthquakes.

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